Abstract: The invention is about the process of determining the vibration of rotor (1) of a rotary machine, by elimination of interference noise signals B, in which is acquired and digitized a signal S emitted by at least one sensor C of the displacement of the rotor (1) of the rotary machine when said rotor is rotating under its normal operating conditions, then is subtracted from it a reference signal B of the same type that has been determined in advance. This process is characterized in that the reference signal B has been acquired at a speed .OMEGA..sub.b of rotor (1) rotation lower than the operating speed .OMEGA. and such that the signals emitted by at least two sensors (C1, C2) of the displacement of the rotor (1), offset at an angle in the same plane perpendicularly to the symmetry axis (A) of said rotor, are nearly identical, ignoring time offset. The invention also concerns the devices designed to implement such a process.